The present invention relates to data networking and more particularly to systems and methods for handling multicast traffic.
Multicast routing techniques have been developed to support a demand for applications such as audio and video conference calls, audio broadcasting, and video broadcasting. In multicast routing, a host sends packets to a subset of all hosts as a group transmission. Multicast routing protocols have been developed to conserve bandwidth by minimizing duplication of packets. To achieve maximum efficiency in delivery of data, rather than being replicated at the source, multicast packets are replicated at the point where paths to multiple receivers diverge.
Multicast techniques have been developed in the context of layer 3 routing technology. Fairly complex protocols have been developed to establish multicast distribution paths so that multicast packets reach interested receivers but do not propagate where they are not needed.
These layer 3 techniques are, however, not applicable to multicast operation within strictly layer 2 networks. In the past, layer 2 networks have been of fairly small scale, e.g., small LANs. Now however, a layer 2 network may include a very large mesh of layer 2 switches. Through tunneling technology, a virtual LAN (VLAN) can be established over a very wide area. There is thus now a desire to push multicast traffic through these large layer 2 networks.
The most common solution is to simply flood the multicast traffic throughout the layer 2 network. This is a highly inefficient use of network resources. Another class of solutions mandates the use of a layer 3 router in direct connection with one of the switches of the layer 2 network. Any layer 3 router switch desiring to receive multicast traffic send join messages towards this router. This layer 3 router is the attraction point for all multicast traffic and the switch that is directly connected to it becomes a common relay point between sources and receivers. This leaves little flexibility in distributing the burden of multicast traffic handling.